Method for providing alloyed zones on a hardfaced workpiece

ABSTRACT

A method for hardfacing a metal workpiece to provide a hardfaced work surface varying in composition over a cross section of the face thereof said method utilizing consumable guide nozzles and electroslag welding procedures.

[ Dec. 11, 1973 United States' Patent 11 1 Bierwith [5 METHOD FORPROVIDING ALLOYED 2,191,469 2/1940 Hopkins......................

ZONES ()N A HARDFACED WORKPIECE 3,665,143 5/1972 Uj11c 3,518,397 6/1970Hannahs [75] Inventor: Stanton F. Bierwith, San Leandro,

Calif.

e y n a t n 0 W uA we S r m i r e 8 .m .m m mx E Ym m m TS PA 0 e h .m Ls d n a S I a nd .m mm C a m mm mm GT m e n b S S A l 3 7Attorney-George L. Church et a1.

Appl. No.: 239,071

ABSTRACT [51] Int. B23h 9/18 [58] Field of Search....................219/146, 145, 137, A metlwd for hardfac'ng metal Pmv'de 219/126, 77 76,73; 37/142; 76/DIG 11, 1; a hardfaced work surface varying incomposition over a cross section of the face thereof said methodutilizing consumable guide nozzles and electroslag welding procedures.

2,191,471 219/76 2 Claims, 6 Drawing Figures PATENTEI] DEC 1 1 I975SHEET 1 BF 3 FIG. 11

FIG. I

FIG. m

PATENTED DEC 1 1 I975 SBEET 3 OF 3 FIG. HZ

EATENIEU I 3.778580 SHIIET 30F 3 FIG. I

34 33 32 a IO FIG. II

METHOD FOR PROVIDING ALLOYED ZONES ON A HARDFACED WORKPIECE BACKGROUNDOF THE INVENTION The present invention relates to a procedure ofhardfacing metal workpieces such as digging tools. In particular thepresent method provides a hardfaced tool having a variation inmetallurgy across the work surface of the tool. More particularly, thepresent invention relates to methods and compositions for manufacturinghardfaced tools utilizing electroslag welding techniques and consumableguide nozzles that are particularly suitable for use in the manufactureof digging tools and the like. The manufacture of tools and implementsused in mining present particular problems to the toolmaking industry.For example, excavator teeth must have a wear surface which has a highresistance to abrasion while at the same time having good tensilestrength properties.

It is generally known in the art that the metallic alloys which providea metalsurface having high resistance to abrasion and wear often arebrittle and deficient in tensile properties. Thus a hardfaced toolhaving outstanding resistance to abrasion and therefore good wearproperties often easily breaks when subject to tension. On the otherhand, tolls hard-faced with metal alloys which have good tensileproperties are often found to be rather poor with regard to resistanceto abration and wear and have a rather short life when subject to useswhere high abrasion and wear are encountered. The prior art providesmany alloy compositions and particular types of forged steel which areproposed to have either good wear properties or resistance to abrasion.Sometools are disclosed to provide a combination of reasonable wearproperties along with good tensile strength properties. a

One method of improving the wear properties of a hardfaced metalworkpiece recently proposed has been hardfacing utilizing theelectroslag welding techniques. One version of a method of providinghardfacing by electroslag welding is provided by B. E. Patent in thetext Electroslag Welding, second Edition, published by the AmericanWelding Society Inc., New York. Particularly on pages 144 to 152 of thistext a procedure for hardfacing a work tool or workpiece is set forth.

Also, in the patent literature, U. S. Pat. No. 2,909,778 to Landis etal. proposes a method of electro arc welding using particular types ofelectrodes. U. S. Pat. No. 2,510,960, U. S. Pat. No. 2,345,758, U. S.Pat. No. 3,325,619, U. S. Pat. No. 3,534,390, U. S. Pat. No. 3,531,620,U. S. Pat. No. 3,491,225, U. S. Pat. No. 3,448,241, U. S. Pat. No.3,215,809 and U. S. Pat. No. 3,118,053 provide particular weldingelectrodes or consumable nozzles particularly suited for electric arcand/or electroslag welding techniques and provide alloys which haveparticularly attractive wear and strength properties. Also, U. S. Pat.No. 3,518,397 to .l. R. Hannahs provides an electroslag weldingtechnique using consumable nozzles wherein metal workpieces can bewelded together to provide a high strength weld.

Also, in the art are U. S. Pat. No. 2,137,471 and U. S. Pat. No.3,023,130 which provide hardfacing techniques using particularelectrodes containing tungsten carbide particles or similar metalcarbide particles which provide hardfaced tools withoutstanding abrasioncharacteristics.

Electroslag welding as mentioned above comprises generally a processwhereby heat is generated by passing an electric arc between electrodesand a ground base. The passing of a current through the electrode meltsthe electrode to provide a weld pool suitable for fusing metal articlestogether or which when properly held in a cavity or gap can provide ahardfacing for the metal workpiece being treated. Recent developments inthe area of electroslag welding have also provided consumable guidenozzles which can be made up of particular metal alloys which when addedto the consumable electrode provide a final hardface alloy which mayhave attractive abrasion resistance and good wear properties.

The consumable guide nozzles disclosed in the art generally comprise asteel tube around which is provided a larger tube containing the metalparticles directed for use in the electroslag welding technique. Thefinal weld on the face of the workpiece contains an alloy of the metalin the electrode wire fed into the electroslag welding apparatus and themetal components which form the consumable guide nozzles used during thewelding process. The consumable guide nozzle also serve the purpose ofdirecting the electrode wire into the slag pool.

One recentinnovation comprises the art of hardfacing digging implementssuch as teeth used in bucketwheel excavators. New applications forbucketwheel excavators such as in the tundra of the frozen north as wellas the tar sand of the frozen north such as those found in Alberta,Canada have made new demands on technology to provide bucketwheelexcavator teeth which have good resistance to abrasion as well as beingable to stand the impact in mining normally experienced undertemperatures of up to -S0F. By the methods of the present invention,hardfaced tools suitable for use in extremes of temperature and abrasionwhile maintaining good wear properties and good tensile strengthproperties have now been provided.

DESCRIPTION OF THE INVENTION The present invention provides a method formanufacturing hardfaced work tools in which the facing on the worksurface of the tool can be custom tailored to provide specificproperties in designated areas of the work surface. Specifically, thepresent invention comprises a method for hard-facing workpieces whichutilizes consumable guide nozzles in electroslag weld hardfacing. Theseconsumable guide nozzles contain particular metal alloy compositionswhich provide the specific metallurgy designed into a particular area ofthe workpiece being manufactured.

It is well known to the art that certain metallic alloy compositions areparticularly resistant to wear and abrasion but are also found to bebrittle and therefore have poor tensile properties. On the other hand,certain metallic alloys used in hardfacing known to have good impact andtensile properties have lesser hardness characteristics and thereforeare not as resistant to abrasion and'wear as the harder more brittlealloys. In the prior art, normally one alloy or the other alloy would beselected in order to provide a hardfacing which had one or the otherdesired properties. In some circumstances, a blend of the components ofeach alloy can be provided to make a hardfaced workpiece having acompromise of all the physical properties required. However, by themethods of the present invention, a

hardfaced workpiece is provided which in effect is custom tailored. Thatis, a hardfaced workpiece is provided which has the particular metallicalloy custom tailored in the hardface to be centered in the area wherespecific characteristics are required. In the present invention, thearea of a tool where the work surface is subject to high abrasion ishardfaced using consumable guide nozzles utilized in electroslag weldhardfacing which contain a metal alloy designed specifically for itsresistance to abrasion. Another area of the same workpiece may requirehigh tensile properties. To meet this requirement, a consumable guidenozzle is provided which contains a high nickel and chrome content.

In carrying out the method of the present invention, electroslag weldingtechniques are preferred. In the process of electroslag welding as usedin the present invention, consumable guide nozzles containing metalalloys designed to make up the final composition of hardfaced elementare selectively provided.

In the electroslag hardfacing technique of the present invention, two ormore consumable guide nozzles can be placed in the area to be hardfacedin order to provide specific metallurgy required in designated areas ofthe hardfaced workpiece. As an example, consumable guide nozzle A isprepared by blending together fine particles passing through a 120screen mesh of 60 percent tungsten carbide, 30 percent ferrochrome, 5percent by weight ferromolybdenum and 5 percent by weight ferrovanadium.This consumable guide nozzle when utilized in electroslag hardfacingtechniques provides a hardface surface area particularly resistantagainst abrasive wear. A second guide nozzle designated as composition Bis prepared by blending 49 percent ferrochrome, 49 percent siliconcarbide and 2 percent cobalt. This nozzle is used in electroslag weldingtechniques of hardfacing in an area where a medium resistance toabrasion is required and where substantial tensile properties arerequired. Nozzle A and nozzle B as disclosed herein when used inhardfacing a workpiece needing the combination of resistance to abrasionand wear as well as high tensile strength properties when properlyapplied to the area where the need is shown can provide a customtailored workpiece having a hardsurfaced area meeting the requirementsfor its use.

Referring to the drawings, FIG. I is a consumable guide nozzle made upof the metallic particle composition known as composition A. FIG. II isa consumable guide nozzle made up of the metallic particle compositionknown as composition B. FIG. III illustrates a bucketwheel excavatortooth having disposed in a cavity or gap formed to provide for thehardfacing of the wear surface of the tooth as shown consumableelectroslag guide nozzles A and B in place for electroslag wledhardsurfacing. FIG. IV illustrates an electroslag welding apparatus wellknown in the art showing consumable guide nozzles A and B in placein thecavity of workiece 10 to be hardfaced. FIG. V illustrates the finishedproduct of workpiece l0 havinga hardfacing on the work surface thereofas shown containing the custom tailored alloy on the surface. FIG. VI isanother vicw ofthe same workpiece in FIG. V illustrating the crosssection of custom tailored metal alloy hardfacing.

By the method of the present invention, a forged or cast steel or othermetal alloy workpiece can be hardfaced in a manner to provide a uniquecustom tailored work surface on that workpiece. Specifically, it hasbeen discovered that by the method of the present invention a workpiecesuch as a bucketwheel excavator tooth used in mining can be hardfaced ina manner whereby the area of the work surface of the tooth which is mostsubject to severe abrasions contains a metallic alloy compositionspecifically designed to have high resistance to abrasive wear. While atthe same time on the same hardfacing in an adjacent section thereto, ametallic alloy is provided which has acceptable wear properties while atthe same time having high tensile properties thereby providing forstrength in the area of the workpiece where it is more specificallyrequired.

By the method of the present invention, a workpiece having a hardfacingon the work surface thereof is provided whereby the hard surfacecomposition is custom tailored to provide the properties most needed inthe particular area of the workpiece. The example given in theillustration of FIGS. I through VII give one embodiment of thisinvention. A bucketwheel excavator tooth having a narrow tip and a broadbase both of which are subject to abrasion is custom tailored so thatthe tip of the tooth having the most severe exposure to abrasioncontains a hardfacing alloy which is most suitable for resistance towear. At the same time, the hardfacing on that tooth also contains analloy toward the center of the tooth where improved tensile strength isrequired. Finally, the base portion of the tooth is hardfaced with ametallic alloy which has high tensile strength.

To better define in detail this embodiment of the methods and thecompositions of the present invention, referring again to the drawings,FIG. I illustrates a consumable guide nozzle which generally cancomprise an elongated outer shell 5 having a hollow tube 6 locatedwithin the shell. The shell is also filled with fine particulate blendof metal alloys 7.

The consumable guide can be of any shape suitable to fit the area to behardfaced. For purposes of the present illustration the consumablenozzle of FIG. I contains the composition disclosed for consumablenozzle A given above and is therefore designated as nozzle A in FIGS. I,II and IV herein presented.

FIG. II illustrates a consumable guide nozzle B similar to that of FIG.I having outer shell 4 and inner hollow tube 8 with the variation thatthe metal particulate composition of 9 which fills outer shell 4 is of adifferent blend of metal particles in order to provide a hardfacecomposition having different physical properties.

FIG. III illustrates a bucketwheel excavator tooth of one type 10 shownin position to be hard surfaced having a depression or gap in the areaof the work surface of the tooth. The depression 19 has disposed thereinconsumable electrodes A and B of FIGS. I and II respectively.

FIG. IV illustrates an electroslag'welding apparatus of the type thatcan be used in providing the custom hardfacing of the present invention.Specifically, in FIG. IV is shown a forged steel excavator tooth l0suitable for use in the bucket wheel excavator used for mining tar sandsor the like. The tooth is placed on workbench II in a position so thatconsumable guide nozzles 15 which are nozzles A and B of FIGS. I and IIrespectively are located within the indentation provided on the worksurface of workpiece 10 to be hardfaced.

Immediately below the consumable nozzles is sump 16 which is adepression in bench 22 nornally provided when electroslag weldingprocedures are employed. Consumable electrode wires 13 are fed throughguide nozzle 15 to the space between the workpiece and heat exchangemeans 17 which can be a copper shoe having a fluid circulatingtherethrough to maintain a certain surface temperature on the heatexchange medium.

In the process of hardfacing by way of electoslag welding as shown inFIG. IV, electrode wire 13 travels through straightening mechanism 20and wire feeding mechanism 21 to the interior of consumable nozzles intothe electroslag tool. Consumable nozzles 15 are releasably connected toextension 14 of the wire feeding mechanism 21. Heat exchange shoe 17 hasa means for coolant inlet and outlet as shown at 18. The placing of theheat exchange means 17 adjacent to the depression in the surface ofworkpiece 10 provides a cavity or .gap to maintain the electroslag weldin the area of the surface of the workpiece to be hardfaced.

Welding current to electrodes 13 is supplied from the conventional powersupply 30 through cables 31 to lugs on extension 23. The power passesthrough the lugs to consumable guides 15 and thereafter through theelectroslag welding pool into workbench 11 and back to the power supplythrough cable 22. The consumable guide nozzles 15 which are also nozzlesA and B can be made to oscillate across the thickness of the cavityformed on workpiece 10 to thereby distribute the heat evenly across thearea being hardfaced as well as provide for a uniform transition ofmetallic alloy from the alloy composition of consumable nozzle A to thealloy composition of consumable nozzle B.

The rate at which electrode 13 is fed into the weld is regulated bycontrol of apparatus 25 which has a connection to the wire feedingmechanism 21 by cable 26. Control apparatus 25 is also provided withmeans to adjust the welding voltage remotely through cable 27 and toregulate through cable 28 the velocity at which the consumable guides 15move across the thickness of the cavity of the workpiece 10. The weldingcurrent is determined by setting the wire speed control. The wire feedmechanism 21 is powered by motor 29 in response to signals from unit 25conducted through connection 26.

A detailed descriptionvof the apparatus shown in FIG. IV is provided inU. S. Pat. No. 3,518,397 issued June 20, 1968. The electroslag weldingtechniques disclosed in this patent reference as well as the electroslagtechnology disclosed in the reference text Electroslag Welding edited byB. E. Patent, American Welding Society, Inc., New York, New York,Reinhold Publishing Corporation, 1962 is suitable for use in the methodof the present invention.

FIG. V illustrates the finished custom tailored hardfaced bucketwheelexcavator tooth 10 suitable for mining tar sands. The composition acrossthe hardface area of workpiece 10 is shown where the metallic alloyconsumable nozzle A is primarily disposed in area 32 of the surfacehardfaced on workpiece l0. Metallic alloy of consumable nozzle B isprimarily provided in area 34 of FIG. V on workpiece 10. In area 33 ofFIG. V there is provided an integration of the alloys of consumablenozzles A and B to provide a transition of the characteristics of eachof the metal alloys of consumable nozzles A and B.

FIG. VI illustrates another view of the same workpiece as shown in FIG.V illustrating the custom tailored hardfacing on the bucketwheelexcavator tooth 10 showing the composition across the area of hardfacingwith the primary alloy of consumable nozzle A being in the area 32 andthat of consumable nozzle B being in the area of 34 with area 33providing an amalgamation of the two alloys to provide for a transitionof the properties of consumable nozzles A and B over the whole of thesurface of the metal workpiece manufactured.

In the preferred embodiment of the method of the present inventionautomatic electroslag welding equipment is employed. Standardelectroslag welding techniques normally practiced in the art and usingan electrode wire of any type from which welding arc is produced underthe shielding of a granular flux are applicable. A filler steel wire ofmetallic alloys desired in part or in whole to provide the hardfacingmatrix on the work face of the tool being hardfaced is also used. Thefiller electrode wire and/or the consumable guide nozzles can becomposed of or contain oxidizing agents such as ferromanganese andferrosilicon. They can also contain denitrifying agents such asferrozircon or slag producing materials for facilitating weldingoperations and for adjusting basicity of the slag in the weld pool.Metals such as nickel chromium, molybdenum, titanium, zirconium andothers are included among the components in the electrode wire and orconsumable nozzles.

Again referring to the drawing in FIG. IV, a metal workpiece such as aforged steel tooth 10 designed for use on a bucketwheel excavator andhaving an indentation on its face is first preheated to a temperature inthe range of 500-l00OF. and more preferably 600-700F. and placed in theproper relation to consumable nozzles 15 which are comprised of acompacted alloy of particles having a size distribution in the range of-140 mesh and each containing the components disclosed for nozzles A andB respectively above. In preparing these nozzles, the metallic particleblends were combined in a sodium silicate liquid carrier, compressedinto the outer shell and the guide tube was inserted through the centerof the filled shell. The whole shell was heated until the silicate boundthe metal particles into a solid mass in the shell. I-Ieat exchange shoe17 is affixed adjacent to the work surface of workpiece l0 and thecavity or gap formed between the cooling shoe and the workpiece providesthe walls in which the electroslag weld pool is formed. About 50 gramsof metal powder of the same alloy as that in electrodes 13 is placed insump 16 in FIG. IV. Electroslag welding is initiated by supplyingelectric power into the electrodes at 55 volts and 400 amps wherein anarc is initiated between the electrode and the powdered metal in thesump. Thereafter 50 grams of flux material is added and the electroslagwelding procedure begun. Electrode wires are fed at a rate to providethat the entire cavity is filled over a period of 5.5 minutes. Theamperage of the electrode is programmed so that during the 5.5 minuteperiod or welding the amperage continually increases in a linear manneruntil it reaches 1,000 amperes at the end of the 5.5 minutes. Thevoltage is programmed to decrease over the same period of time until itreaches 32 volts at the end of 5.5 minutes. The consumable nozzles areoscillated across the face of the workpiece at the rate of 6oscillations per minute. At the end of the welding step a forgedbucketwheel excavator tooth having a custom tailored hardfaced worksurface is recovered.

The invention claimed is:

l. A method for hardfacing a metallic workpiece to provide saidworkpiece with a hardfaced work surface having a variedmetallurgicalcomposition thereover comprising the steps of:

a. placing the work surface to be hardfaced in a vertical position;

b. placing a heat exchange means adjacent and complementary to said worksurface to form a gap and retain molten weld metal therebetween;

c. placing adjacent to one area of the work surface within said gap aconsumable guide nozzle having means for passing a consumable electrodewire therethrough said consumable guide nozzle containing apredetermined metallurgical composition comprised of fine metalparticles adhered to a ho]- low metal guide tube;

d. placing adjacent to a contiguous area of the same work surface ofsaid workpiece, a second consumable guide nozzle having means forpassing a consumable electrode wire therethrough said second guidenozzle containing a different predetermined metallurgical compositionfrom that of said first guide nozzle said metallurgical compositioncomprised of fine metal granules adhered to hollow metal guide tube;

e. feeding an electrode wire through each consumable guide nozzle;

f. passing an electrical current through said electrode wires to depositweld metal and concurrently melt said consumable guide nozzles andpositioning said first and second guide nozzles so that upon meltingsaid first and second guide nozzles form separate zones of differentmetalurgical composition fused to the surface of the workpiece andconnected by a fused zone of a metalurgical composition formed by ablending of the melted metal from said first and second guide nozzles.

2. A method according to claim 1 wherein the workpiece is a bucketwheelexcavator tooth.

1. A method for hardfacing a metallic workpiece to provide saidworkpiece with a hardfaced work surface having a varied metallurgicalcomposition thereover comprising the steps of: a. placing the worksurface to be hardfaced in a vertical position; b. placing a heatexchange means adjacent and complementary to said work surface to form agap and retain molten weld metal therebetween; c. placing adjacent toone area of the work surface within said gap a consumable guide nozzlehaving means for passing a consumable electrode wire therethrough saidconsumable guide nozzle containing a predetermined metallurgicalcomposition comprised of fine metal particles adhered to a hollow metalguide tube; d. placing adjacent to a contiguous area of the same worksurface of said workpiece, a second consumable guide nozzle having meansfor passing a consumable electrode wire therethrough said second guidenozzle containing a different predetermined metallurgical compositionfrom that of said first guide nozzle said metallurgical compositioncomprised of fine metal granules adhered to hollow metal guide tube; e.feeding an electrode wire through each consumable guide nozzle; f.passing an electrical current through said electrode wires to depositweld metal and concurrently melt said consumable guide nozzles andpositioning said first and second guide nozzles so that upon meltingsaid first and second guide nozzles form separate zones of differentmetalurgical composition fused to the surface of the workpiece andconnected by a fused zone of a metalurgical composition formed by ablending of the melted metal from said first and second guide nozzles.2. A method according to claim 1 wherein the workpiece is a bucketwheelexcavator tooth.